As to a single physical system (such as an atom, a molecule, or an ion) three-dimensionally distributed in a material, a cofocal laser microscope is well-known as an apparatus for observing a position or a state of the single physical system. For example, the cofocal laser microscope is described in “Mechanism and Application of Optical device”, p 70-73, published by Optronics.co.jp, 2003. In this microscope, a laser is converged by a first lens, a fluorescence radiated from some material positioned at a focus is converted to a parallel-light by the first lens, and the parallel-light is converged by a second lens. By locating a pin-hole at a focus of the second lens, the fluorescence is detected behind the pin-hole. As a result, from the focus (converged by the first lens) having a size three-dimensionally similar to the wavelength, the fluorescence is only detected. Accordingly, by scanning a focal position (converged by the first lens), a position of a fluorescent material in the material can be three-dimensionally examined.
However, in this method, following two defects are included.
(1) This microscope is only applied to a physical system radiating a strong fluorescence.
(2) In case of a single quantum system, this microscope is only applied to an object quickly repeating an excitation and a relaxation (radiating the fluorescence) with the same laser wavelength.
For example, this microscope cannot be applied to a molecule changing with an optical excitation, or a molecule, an atom and an ion each of which population moves to a state different from an initial state.
In the material, as to a physical system having a weak fluorescence (or not radiating the fluorescence), or a single physical system (such as a rare earth ion in a crystal) generating only one photon at a first excitation (by changing after the first excitation or by moving the population), a position and a state cannot be three-dimensionally observed. Briefly, an apparatus and a method for observing the position and the state with high sensitivity and high spatial resolution (similar to the wavelength) are not known yet.